Facile meso to rac Isomerization of the Bis-Planar Chiral Ferrocenyldiphosphine Bis(1-(diphenylphosphino)-η⁵-indenyl)iron(II)

Abstract

The meso isomer of the ferrocenyldiphosphine bis(1-(diphenylphosphino)-η 5 -indenyl)iron(II) isomerizes to the rac isomer overnight in tetrahydrofuran at room temperature. The isomerization is accelerated by salts but does not occur in chloroform solvent.

Structure–molecular orbital energy correlations in Me3Si-substituted bis(indenyl)iron complexes evidenced with UV–vis spectroscopy and cyclic voltammetry

“…Despite the fact that ferrocene is one of the most intensively investigated organometallic compounds, having been studied with a broad variety of spectroscopic, electrochemical and other methods, data and results of respective studies of the related bis(indenyl) iron sandwich [1] (beyond some spectroscopic and electrochemical data of the unsubstituted parent compound [2]) are absent, because these complexes could only be successfully synthesized recently [3][4][5][6]. The chemistry, including electrochemical and spectroscopic data, of the related titanium compounds has been the subject of a recent report [7].…”

Synthesis, structures and rac/meso isomerization behaviour of bisplanar chiral bis(phosphino-η5-indenyl)iron(II) complexes

“…Reagent grade solvents were dried and distilled prior to use: diethyl ether and tetrahydrofuran from Na/benzophenone; dichloromethane and petroleum ether (50-70°C fraction) from CaH 2 . Diphenylphosphinoindene [16], bis(1-(diphenylphosphino)-g 5 -indenyl)iron(II) [3,14], 1-methylindene [22] and 4,7-dimethylindene [23] were prepared by published procedures. 1,2-dimethylindene and 1,4,7-trimethylindene were prepared from 2-methylindene and 4,7-dimethylindene, respectively, by modifications of the route used to prepare 1-methylindene.…”

“…At 23°C, k obs ¼ 1:59ð3Þ Â 10 À5 s À1 [14,15]. The isomerization does not go to completion, indicating that the reverse process of rac to meso isomerization does occur, but with a slower rate constant.…”

“…The number of non-ansa diindenyl iron complexes that have been crystallographically characterised to date is remarkably small [4,[10][11][12][13]. Further studies on [(1-PPh 2 -g 5 -C 9 H 6 ) 2 Fe] have shown that this indenyl ferrocene undergoes a facile isomerization in THF from the meso isomer to the rac isomer at ambient temperatures [14,15]. Deuterium labeling studies, crossover experiments, activation parameter measurements (including the activation volume), salt and solvent effects all point to a mechanism involving THF coordination, indenyl ring-slippage, and indenide dechelation with phosphine coordination to give a zwitterionic intermediate.…”

“…We report here the preparation, isolation and structure of a number of methyl and trimethylsilyl derivatives. Some of this work has previously been communicated [14].…”